There are a number of patents and reports, which are noted below, which teach a variety of two splitter optical coherence tomography configurations. However, a difficulty that arises from nearly all of the prior devices is that there may be significant loss in the optics of the devices, and that there may be significant noise introduced into the device. Low losses in the OCT apparatus are required because of the low amplitude of the signal which is returned from the object or tissue that has been scanned. Moreover, OCT typically employs light sources which have significant bandwidth, giving rise to the presence of excess photon noise along with other noise items and sources such as shot noise and thermal noise.
Thus, an ideal OCT configuration should have low losses, while achieving good extinction or suppression of excess photon noise and/or derivations thereof, shot noise, and so on. In order to apply noise reduction, balance detection is employed, which requires an OCT configuration having a two splitter configuration.
It has been noted that a number of patents, which are identified below present various two splitter configurations, particularly for purposes of balance detection, but they pay little or no attention to the particular choice of splitting ratio of the splitters so as to minimize loss or to the particular choice of optical splitters to minimize the stray reflections in order to maximize the signal to noise ratio, and to allow multiple and versatile functionality.
As a practical matter, single mode couplers are preferred in OCT apparatus for routing the signal in order to project and define a desirable and controllable area or line on the target or object to be scanned. However, reflection from the end of the fiber leads may return light back into the system, thereby generating noise, and preventing the system from being used in a confocal scanning regime when the path of the reference beam is blocked.
In keeping with a particular aspect of the present invention, an improved optical mapping apparatus is provided which employs a bulk beam splitter having an optimized splitting ratio. A beam splitter having fiber input and output may be employed.
Thus, in a first aspect of the present invention, there is provided a two splitter OCT configuration which is powered by an optical radiation source having a large bandwidth, whereby balanced detection is achieved.
A second aspect of the present invention provides for an optical mapping apparatus having an OCT system which is built around a bulk beam splitter, wherein an input beam is split into an object beam and a reference beam, and where the object beam and reference beam are combined in a single mode fiber coupler.
As will be noted hereafter, a third aspect of the present invention provides methods and apparatus whereby en-face images of different depth resolution may be sequentially displayed.
A fourth aspect of the present invention discusses methods and apparatus which are sensitive to polarization of light returned from the object being scanned.)
In a fifth aspect of the present invention, methods and apparatus are discussed which can deliver, sequentially or quasi-sequentially, OCT images and confocal microscopy images.